Process of separating soap stock



Patented May 13, 1941 H. Thurman, Bronxville, N. Y.', assignors to.Refining, Inc., Reno, Nev., a corporation of Nevada No Drawing.Application October 5, 1937,

Serial No. 167,470

, 8 Claims. (01.

This invention relates to a method of centrifugally separating soapstock from glyceride oils which have been treated with an alkalineindustry has been confronted with the necessity of shutting down thecentrifugal separator intermittently in order to clean the bowl thereof,since a layer of soap stock, almost invariably,

progressively builds up in the centrifugal bowl against the outer wallthereof. When this layer reaches a thickness at which clean separationbetween the soap stock and the oil no longer takes place, thecentrifugal must be dismantled and the layer scraped from the bowl.Ordinarily such a cleaning operation must be performed every few hoursand seriously reduces the total output of a refining operation employingcentrifugals.

Even before it becomes necessary to shut down the centrifugal forcleaning purposes, the increasing layer reduces the capacity ofthe-centrifugal so as to progressively decrease the amount of oil andsoap stock that may be passed therethrough. Not only is the cubiccontent of the bowl reduced, but the neutral zone of separation isprogressively moved toward the center of the centrifugal so as to cutdown the centrifugal force causing separation. As the layer builds up,soap stock begins to discharge with the refined oil and when the amountof soap stock discharging therewith reaches a quantity' which can nolonger be tolerated, the machine is stopped and cleaned. Even beforethis happens, the force tending to push the layer of soap soap stockoscillate in'the centrifugal so that soap stock is intermittentlydischarged with the refined oil and the refined oil, is intermittentlydischarged with the soap stock. Thus there is constant danger of therefined oil being contaminated with soap stock even before the neutralzone is shifted far enough to cause soap stock to be dischargedcontinuously with the refined oil.

The above discussed layer of soap stock is predominantly made up of thegummy, pr'oteinaceous constituents of thesoap stock. Certain of theseconstituents adhere to the outside wall of the centrifugal bowl, thenother particles of the same material cohere to those already adhered tothe bowl wall. The resultant layer is a sticky, gummy material which isextremely difilcult to clean from the bowl wall and is frequently calledliver in the art because of its appearance and consistency. Applicanthas found that if the initial adherence of this gummy material to thewall of the bowl can be prevented, the layer will no longerbuild up.This initial adherence is promoted by the refrigerating effect of arapid rotating centrifugal bowl in contact with the atmosphere.Separation of soap stock from glyceride oil is ordinarily carried on ata temperature considerably above room temperature. Contact between thecentrifugal bowl and gases at room temperature cool-the walls of thebowl and therefore the material in contact therewith. The initialadherence of the gummy particles to the wall of the bowl may beprevented by applying heat externally to the wall of the bowl orsupplying a heating medium internally of the I bowl in order tocompensate for this loss of heat 'or even raise the temperature of thematerial November 23, 1937.

In accordance with the present. invention this initial adherence mayalso be prevented by incorporating an anti-sticking agent with thematerials being separated so that the tendency of the gummy particles tostick to the wall of the bowl is overcome. Certain materials, hereinafter described, appear to render the gummy particles les's sticky, orproduce a layer of material adjacent the outer wall of the bowl .whichprevents the sticky materials coming into con tact therewith.

It is, therefore, an object of the present invention to provide aprocess of centrifugally -separating soap stock and glyceride oils inwhich an anti-sticking agent is employed for preventing initialadherence of gummy or sticky materials contained in soap stock to theouter wall of the centrifugal bowl.

It is a further object of the present invention to provide a process ofseparating soap stock from glyceride oil employing an anti-stickingagent to eliminate or reduce the heating of the centrifugal bowl for theprevention of the building up of a layer of soap stock therein.

The anti-sticking agents of the present invention may be introduced intothe process so that they are present in the materials adjacent the outerwall of the centrifugal during centrifugal separation. Ordinarily theanti-sticking agent is introduced into the process some time prior tocentrifugal separation so that it will be thoroughlyadmixed with all ofthe materials undergoing separation, but it is within the contemplationof the present invention to introduce such an antisticking agent intothe centrifugal bow; so that it contacts and mixes with only theseparated soap One anti-sticking agent which has been successfullyemployed is karaya gum. This material may be introduced into the processat any time prior to separation or into the centrifugal itself as abovedescribed. It is relatively inert with respect to the substancesemployed in the refining operation and may therefore be mixed eitherwith the refining solution or the oil prior to refining or it may beinjected into the mixing zone wherein the refining solution and oil aremixed. Also, it may be injected into the mixture of oil and soap stockbeing delivered to the centrifugal or, as indicated above, directly intothe centrifugal bowl adjacent the outer periphery thereof. This materialappears to render gummy particles of the soap stock less adherent to thewalls of the bowl and to also provide a thin layer of material on thewalls of the bowl to which the said particles will not adhere.

The karaya gum separates with the soap stock so as not to contaminatethe neutral oil, and the nature of this material along with the smallamounts necessary for performing the anti-sticking function does notimpair the value of the soap stock. It is, therefore, unnecessary toseparate the karaya gum from the soap stock.

Other anti-sticking agents which may be employed are certain alcohols,for example, those which are sufliciently volatile to be recovered fromthe soap stock and oil. Aliphatic monohydric alcohols having less thansix carbon atoms, for example, ethyl, butyl, iso-propyl, propyl and amylare satisfactory. Also the esters, for example the acetic esters of suchalcohols, as well as certain polyhydric alcohols having the requisitevolatility and their esters, can be employed. Thesematerials arepreferably admixed with either the oil or the refining solution prior torefining or in,- jected into the mixing zone, since they also have anadditional function of reducing the saponification of neutral oil duringthe neutralization step. However, they perform their anti-stickingfunction even if mixed with the materials entering the centrifugal orwith the soap stock in the bowl after it has been separated from theoil.

Also, the alcoholates, such as sodium or potassium alcoholates, may beemployed as the antisticking agent since such compounds liberate alcoholand caustic alkali upon contact with water. For this reason thealcoholates are preferably added with the alkaline refining solution oradded in the mixing zone for therefining solution and glyceride oil. Thealcohol liberated from the alcoholates upon contact with the water ofthe refining solution also functions as inhibitors for thesaponification of material during the neutralization step as is the casewhen alcohols are added as the anti-sticking agent.

Furthermore, the alcohols, either those originally added or thoseliberated from the alcoholates, have the additional function of cuttingdown the entrainment of neutral oil in the soap stock during separation;However, the amount of these materials necessary to prevent sticking isconsiderably smaller than the amount necessary to substantially inhibitthe saponification of neutral oil and the entrainment of neutral oil inthe soap stock, although the employment of larger quantities does notinterfere with the prevention of adherence of soap stock to the walls ofthe centrifugal bowl. The major portion of the alcohols discharge fromthe centrifugal with the soap stock. This portion, as well as the smallportion discharging with the refined oil, may be recovered, if desired,for re-use in the process by vaporizing the alcohol and then condensingit.

Other agents which may be employed to prevent sticking are relativelyconcentrated aqueous solutions of salts which have no deleteriousreaction with the soap stock or neutral oil and which have highsolubility in water. Alkaline metal salts are in general suitable, suchas sodium sulphate, chloride acetate, carbonate and silicate, as well asthe equivalent potassium salts. These materials should be, in mostcases, added to the process subsequent to the neutralization step, sincetheir presence is undesirable during the neutralization step. They maybe mixed with the materials being delivered to the centrifugal or theymay be delivered into the centrifugal bowl so as to mix only with thesoap stock adjacent the outer periphery thereof. Since these materialshave a much greater specific gravity than the soap stock, they provide alayer of material between the soap stock and the outer wall of thecentrifugal bowl so that the gummy materials contained in the soap stockare prevented from contact with the outer walls. These materials willalso function to make the soap stock heavier and cause it to more easilyseparate from the refined oil if they are used in sufficient amounts.The amount necessary to prevent sticking and building up of a layer ofsoap stock in the centrifugal bowl is considerably lessthan thatrequired for substantially increasing the weight of the soap stockcolumn in the centrifugal, although larger quantities do not interferewith the prevention of sticking.

Mixtures of the various materials above mentioned may also be employedas the anti-sticking agent. As to the amount of the various materialswhich should be employed, it is impossible to give definite figures.This amount will depend upon the type of oil being refined and theamount of gummy materials present in the oil. Ordinarily a very smallamount, less than 1% of the oil being refined, is sufficient although,as hereinbefore indicated, larger quantities may be employed.

The process of the present invention is particularly adapted foremployment with continuous processes of refining glyceride oils since acentrifugal separator is ordinarily employed therewith. However, it maybe employed whenever soap stock is separated from glyceride-oilsirrespective of whether the neutralization to produce the soap stock hasbeen effected by a continuous mixing or a batch mixing step andirrespective of whether the oil is heated prior to the neutralization orthe mixture is heated subsequently to the neutralization.

By the use of the term anti-sticking agent, as employed in the claims,we intend to define and embrace and be restricted to an agent, inaddition to the neutralizing reagent which is introduced to the mixtureand functions to prevent the adherence of the sticky components of thesoap stock to the centrifugal bowl and the building up of a layer knownin the art as liver" which shifts the neutral. zone and thus preventsclean separation of the soap stock and the oil, necessitating frequencyof shutdowns; and the term is likewise restricted to an agent which willhave no deleterious reaction or efiect upon the soap stock or theneutral oil and, moreover, of a character which will not interfere withthe reaction between the neutralizing agent and the fatty. acids andother impurities contained in the crude oil being refined.

While we have described the preferred emboditrifugal bowl in which thesoap stock collects ad-" jacent the outer wall of the bowl prior tobeing discharged therefrom and constituents of the soap stock tend toadhere to said wall of the bowl,

stock and glyceride oil to a rapidly rotating centrifugal bowl in whichthe soap stock collects adjacent the outer wall of the bowl prior tobeand separately discharging said soap stock from prevent saidconstituents from adhering to said wall.

2. In the process of continuously separating soap stock from alkalitreated glyceride oils,

which includes, delivering a mixture of said soap stock and glycerideoil to a rapidly rotating cen trifugal bowl in which the soap stockcollects' adjacent the outer wall of the bowl prior to being dischargedtherefrom and constituents of the soap stock tend to adhere to said wallof the bowl, and separatelydischarging said soap stock from said bowl,the improvement which comprises, incorporating an anti-sticking agentcomprising karaya gum with at least said soap stock adjacent the wall ofsaid bowl to prevent said constituents from adhering to said wall.

3. In the process of continuously separating soap stock from alkalitreated glyceride oils which includes delivering a mixture of said soapstock and glyceride oil to a rapidly rotating centrifugal bowl in whichthe soap stock collects the soap stock tend to adhere to said wall ofthe bowl, and separately discharging said soap stock from said bowl, theimprovement whichcomprises, incorporating an anti-stickingagentlcomprising a relatively concentrated aqueous solution of a watersoluble saltof an alkali metal with at least said soap stock adjacentthe wall of said bowl to prevent said constituents from adhering to saidwall.

5. The process of continuously separating soap stock from a glycerideoil previously treated with an alkaline refining agent, which comprises,delivering a mixture of saidsoap stock and oil to a rapidly rotatingcentrifugal bowl, incorporating with said mixture prior to deliveringthe same into said bowl an anti-sticking agent for preventing theadherenceof constituents of said soap stock to the outer wall of thebowl, whereby said soap stock will substantially uniformly dischargefrom said bowl, and separately discharging said soap stock and said oilfrom said bowl.

6. The process of continuously separating soap stock from a glycerideoil previously treated with an alkaline refining agent, which comprises,delivering a mixture of said soap stock and oil to a rapidly rotatingcentrifugal bowl, incorporating with said mixture prior to deliveringthe same into saidbowl an anti-sticking agent comprising karaya gum forpreventing the adherence of constituents of said soap stock to the outerwall of. the bowl whereby said soap stock I will substantially uniformlydischarge from said bowl, and separately discharging said soap stock andsaid oil from said bowl.

'7. The process of continuously separating soap the same into said bowlan anti-sticking agent comprising an aliphatic monohydric "alcoholhaving less than six carbon atoms for preventadjacent the outer wall ofthe bowl prior to besoap stock from alkali treated glyceride oils whichincludes delivering a mixture of said soap ing the adherence ofconstituents of said soap stock to the outer wall of the bowl, wherebysaid soap stock will substantially uniformly discharge from said bowl,and separately discharging said soapstock and said oil from said bowl.

'8. The process of continuously separating soap stock from a glycerideoil previously treated with an alkaline refining agent, which comprises,delivering a mixture of said soap stock and oil to a rapidly rotatingcentrifugal bowl, incorporating with said mixture prior to deliveringthe same into said bowl an anti-sticking agent comprising a relativelyconcentrated solution of a water soluble salt of an alkali metal for preventing the adherence of constituents of said soap stock to the outerwall of the bowl, whereby said soap stock will substantially uniformlydischarge from said bowl, and separately discharging said soap stock andsaid oil from said bowl.

BENJAMIN CLAYTON. BENJAMIN H. 'IH'URMAN.

